I have a rule whose output files are symbolic link files. Even though the link files are being made, Snakemake exits with a MissingOutputException and lists the output files as being missing. If instead of making a symlink with "ln -s" I copy the files with "cp -p" it works. I tried increasing the --latency-wait but it made no difference.
Sounds like you are using relative path for source file when symlinking. Use absolute path.